#box1 {
    width: 100px;
    height: 100px;
    background-image: url("../imgs/aa.ico");
    background-size: 100% 100%;
}

#box2 {
    width: 100px;
    height: 100px;
    background-image: url("../imgs/bb.png");
    background-size: 100% 100%;
}

#box3 {
    width: 100px;
    height: 100px;
    background-image: url("../imgs/cc.svg");
    background-size: 100% 100%;
}